gatekeeper HAL uses "default" service name

The getService() and registerAsService() methods of interface objects
now have default parameters of "default" for the service name. HALs
will not have to use any service name unless they want to register
more than one service.

Test: builds

Bug: 33844934
Change-Id: Ie49c8cea290d328b2160f6012e7c143c49d535cc

gatekeeperd/gatekeeperd.cpp

@@ -56,7 +56,7 @@ static const String16 DUMP_PERMISSION("android.permission.DUMP");
 class GateKeeperProxy : public BnGateKeeperService {
 public:
     GateKeeperProxy() {
-        hw_device = IGatekeeper::getService("gatekeeper");
+        hw_device = IGatekeeper::getService();
 
         if (hw_device == nullptr) {
             ALOGW("falling back to software GateKeeper");